U.S. patent application number 12/244162 was filed with the patent office on 2009-02-12 for optical pickup and optical information processing apparatus.
Invention is credited to Hideaki Hirai.
Application Number | 20090040908 12/244162 |
Document ID | / |
Family ID | 35425055 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090040908 |
Kind Code |
A1 |
Hirai; Hideaki |
February 12, 2009 |
OPTICAL PICKUP AND OPTICAL INFORMATION PROCESSING APPARATUS
Abstract
An optical pickup performing recording, reproduction and
deletion of information on or from an optical recording medium. The
pickup includes light sources for information recording media using
a blue wavelength beam, information recording media of DVD family
and information recording media of CD family. A single object lens
may be used to condense light from any of the light sources. A
single aberration correction device may be disposed in a common
light path between each of the light sources and the object
lens.
Inventors: |
Hirai; Hideaki;
(Yokohama-shi, JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1825 EYE STREET NW
Washington
DC
20006-5403
US
|
Family ID: |
35425055 |
Appl. No.: |
12/244162 |
Filed: |
October 2, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11138519 |
May 27, 2005 |
7450486 |
|
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12244162 |
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Current U.S.
Class: |
369/112.23 ;
G9B/7 |
Current CPC
Class: |
G11B 7/1367 20130101;
G11B 7/139 20130101; G11B 7/13925 20130101; G11B 2007/0006
20130101; G11B 7/1275 20130101 |
Class at
Publication: |
369/112.23 ;
G9B/7 |
International
Class: |
G11B 7/00 20060101
G11B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2004 |
JP |
2004-159641 |
Claims
1-16. (canceled)
17. A wavelength selectable deflecting element for deflecting light
having wavelengths .lamda.1, .lamda.2, and .lamda.3, said
wavelengths .lamda.1, .lamda.2, and .lamda.3 respectively
corresponding to optical recording mediums having substrate
thicknesses t1, t2, and t3, wherein t1<t2<t3 and
.lamda.1<.lamda.2<.lamda.3, said wavelength selectable
deflecting element emitting a zero-order deflected light beam when
light having the wavelength .lamda.1 is incident, and said
wavelength selectable deflecting element emitting a 1st-order
deflected light beam when light having the wavelength .lamda.2 or
.lamda.3 is incident.
18. The wavelength selectable deflecting element of claim 17,
further comprising: a first side having a first deflecting pattern
for canceling spherical aberration in the respective optical
information recording medium when light having the wavelength
.lamda.2 is incident; and a second side having a second deflecting
pattern for canceling spherical aberration in the respective
optical information recording medium when light having the
wavelength .lamda.3 is incident.
19. The wavelength selectable deflecting element of claim 17,
wherein said wavelength selectable deflecting element emits a
1st-order deflected light beam that is scattered to avoid
overlapping a focused light spot when light having one of the
wavelengths .lamda.2 or .lamda.3 is incident.
20. The wavelength selectable deflecting element of claim 17,
wherein the wavelength selectable deflecting element has a coating
area to transmit light having the wavelengths .lamda.1 and .lamda.2
and reflect light having the wavelength .lamda.3.
21. The wavelength selectable deflecting element of claim 17,
wherein the wavelength selectable deflecting element has a coating
area to transmit light having the wavelengths .lamda.1 and .lamda.3
and reflect light having the wavelength .lamda.2.
22. The wavelength selectable deflecting element of claim 17,
wherein a deflecting pattern of the wavelength selectable
deflecting element is designed to cancel coma aberration.
23. The wavelength selectable deflecting element of claim 17,
wherein a shift pattern of at least one aberration correction phase
shifter area for one of wavelengths .lamda.2 and .lamda.3 on the
wavelength selectable deflecting element is designed to cancel
spherical aberration.
24. An optical pickup which performs at least one of recording,
reproduction and deletion of information on or from at least three
optical recording media having respective substrate thicknesses of
t1, t2, and t3, wherein t1<t2<t3, said pickup comprising: a
light source of a wavelength .lamda.1 for the optical recording
medium which has the substrate thickness of t1, a light source of a
wavelength .lamda.2 for the optical recording medium which has the
substrate thickness of t2, and a light source of a wavelength
.lamda.3 for the optical recording medium which has the substrate
thickness of t3, wherein .lamda.1<.lamda.2<80 3; an object
lens which condenses light from the light sources; and a wavelength
selectable deflecting element which emits a zero-order deflected
light beam when light having the wavelength .lamda.1 is incident,
and which emits a 1st-order deflected light beam when light having
the wavelength .lamda.2 or .lamda.3 is incident.
25. The optical pickup of claim 24, wherein the wavelength
selectable deflecting element comprises: a first side having a
first deflecting pattern for canceling spherical aberration in the
respective optical information recording medium when light having
the wavelength .lamda.2 is incident; and a second side having a
second deflecting pattern for canceling spherical aberration in the
respective optical information recording medium when light having
the wavelength .lamda.3 is incident.
26. The optical pickup of claim 24, wherein light from the light
source of the wavelength .lamda.3 is incident on the wavelength
selectable deflecting element with an infinite system.
27. The optical pickup of claim 24, wherein the wavelength
selectable deflecting element has a coating area to transmit light
having the wavelengths .lamda.1 and .lamda.2 and reflect light
having the wavelength .lamda.3.
28. The optical pickup of claim 24, wherein the wavelength
selectable deflecting element has a coating area to transmit light
having the wavelengths .lamda.1 and .lamda.3 and reflect light
having the wavelength .lamda.2.
29. The optical pickup of claim 24, wherein said wavelength
selectable deflecting element emits a 1st-order deflected light
beam that is scattered to avoid overlapping a focused light spot
when light having one of the wavelengths .lamda.2 or .lamda.3 is
incident.
30. An optical information processing apparatus comprising the
optical pickup of claim 24, said apparatus performing at least one
of recording, reproduction and deletion of information using at
least one light beam having the wavelength of .lamda.1, .lamda.2 or
.lamda.3.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an optical pickup and an
optical information processing apparatus using the optical pickup
by which a satisfactory beam spot on an information recording
surface of a blue-system optical recording medium which uses a
light source of a blue wavelength zone, to a DVD-system optical
recording medium using a light source of a red wavelength zone, or
to a CD-system optical recording medium using a light source of an
infrared wavelength zone.
[0003] 2. Description of the Background Art
[0004] Optical recording media, such as a CD with a storage
capacity of 0.65 GB and a DVD with a storage capacity of 4.7 GB,
are known as means to store image information data, voice
information, or computer data. Further, demands for further
improvement in recording density and storage capacity have become
stronger in recent years. Specifically, the necessity for storage
capacity such as 22 GB by which a high-definition television
program can be stored for two hours for recording one movie
program, or for 44 GB by which the same can be stored for four
hours for recording a sports relay broadcast or the like.
[0005] In an optical pickup which performs information writing or
informational reading to/from an optical recording medium, in order
to improve the recording density of such an optical recording
medium, it is effective to reduce the diameter of the beam spot.
The beam spot may be formed by a beam condensed by an object lens
and formed on an optical recording medium by enlarging the
numerical aperture (which may be abbreviated as `NA`) of the object
lens, or by shortening the wavelength of the light emitted by a
light source. Therefore, for example, in a "DVD-system optical
recording medium" with which high recording density is achievable
for which the NA of the object lens is 0.65 and the light source
emits 660 nm wavelength light in comparison to a "CD-system optical
recording medium" for which the NA of the object lens is 0.50 and
the light source emits 780 nm wavelength light.
[0006] As for such an optical recording medium, as mentioned above,
further improvement in the recording density and storage capacity
is demanded, and, for this purpose, it is desirable to increase the
NA of the object lens (i.e., make the NA greater than 0.65), or to
make the wavelength of the light source shorter than 660 nm.
[0007] There are several new standards for optical recording media.
One known standard is the "HD-DVD" standard. It uses a light source
with an operating wavelength of 405 n-m and an object lens with an
NA of 0.65 for an optical recording medium having a
light-incidence-side substrate with a thickness of 0.6 mm. Another
known standard is the "Blu-ray Disc" standard. The latter standard
uses a light source with an operating wavelength of 405 nm and an
object lens with an NA of 0.85 for an optical recording medium
having a light-incidence-side substrate with a thickness of 0.1
mm.
[0008] Another problem is that users still have conventional
recording medium such as CDs and DVDs. It is desirable that these
conventional optical recording media and new optical recording
media according to the above-mentioned new standard should be
handled with a single common optical information processing device.
A relatively easy method of solving this problem is that an optical
pickup according to the conventional standard and an optical pickup
according to the new standard are both mounted in one machine
separately. However, this method may raise the cost or increase the
size of the whole machine.
[0009] Thus, problems to be solved occurring when achieving an
optical pickup directed to future high-density optical recording
media are to reduce aberrations which otherwise increase due to
increase in NA or reduction in wavelength, and, also, to achieve
compatibility between the conventional standard and the new
standard optical recording media (i.e., of different generations).
Further, it is also a problem to be solved to achieve these objects
without a remarkable increase in size/costs of the machine.
[0010] Furthermore, as described above, as long as the conventional
recording media such as CDs and DVDs are applied, spherical
aberration occurring in connection with a thickness error of the
optical recording medium may be reduced by improving the
manufacturing accuracy of the optical recording medium. Further,
coma aberration in connection with an inclination of an optical
recording medium may also be reduced by setting the substrate
thickness at 0.1 mm, even when the light source of a blue
wavelength zone and an object lens NA of 0.85 are applied.
[0011] However, in the future, in connection with achievement of
high-speed rotation of an optical recording medium, application of
a multi-layer-type optical recording medium, which will be
described later, and also application of a multi-level recording
scheme, it may not be possible to tolerate such aberration, and
thus, a special scheme for correcting it should be needed.
[0012] For the above described problem, it is preferable to use
three light sources for blue-system, DVD-system and CD-system
optical recording medium with a single object lens for focusing an
incident light beam from each light source. But there is a problem
about aberration to focus for each blue-system, DVD-system and
CD-system optical recording medium with a single object lens. For
example, in the case of using a single object lens, which is
designed for minimizing the wavefront aberration when it is used
with an infinite optical system (a parallel beam is incident to the
object lens) and with a blue-system optical recording medium
(.lamda.1=405 nm, NA(.lamda.1)=0.67, substrate thickness t1=0.6
mm), for focusing a beam spot on a DVD recording medium
(.lamda.2=660 nm, NA(.lamda.2)=0.65, substrate thickness t2=0.6
mm), there arises a spherical aberration shown in FIG. 2B due to
the difference in the wavelength. At this point, the horizontal
axis of FIG. 2B represents the distance from the optical axis, and
the vertical axis of FIG. 2B represents wavefront aberration.
[0013] As in the above described case, in the case of using a
single object lens, which is designed for minimizing the wavefront
aberration when it is used with an infinite optical system and with
a blue-system optical recording medium (.lamda.1=405 nm,
NA(.lamda.1)=0.67, substrate thickness t1=0.6 mm), for focusing a
beam spot on a CD recording medium (.lamda.=785 nm,
NA(.lamda.3)=0.50, substrate thickness t3=1.2 mm), there arises a
spherical aberration shown in FIG. 2C due to the difference in the
wavelength and also due to the difference in the thickness. To
reduce such a spherical aberration, it is known to use a finite
optical system (a non-parallel beam is incident on the object lens)
as described in Japanese Patent No. 3240846. Generally, changing
the divergence angle of the beam that is incident on the object
lens is the same as changing the spherical aberration. A beam
divergence angle may be selected to reduce the spherical
aberration. For example, the wavefront aberration can be suppressed
when the object distance of the CD optical system (the distance
between the optical source and the object lens) is changed.
[0014] FIG. 3B shows the relationship between the object distance
and the wavefront aberration. It is indicative of deterioration at
the wavefront surface. As shown in the drawings, the deterioration
at the wavefront surface is decreased around 50 mm of object
distance. Although FIG. 3 shows no parts between the object lens
and the light source, actually there are a wavelength plate, a
prism and a lens, etc. between the object lens and the light
source. In particular, an optical pickup corresponding to three
kinds of optical discs (blue-system, DVD-system and CD-system) has
a lot of parts, so the above described 50 mm of object distance is
too short. It is a limitation for parts alignment. And coma
aberration occurs from object lens shifts with tracking movement or
focusing movement in the finite system.
[0015] According to the background art, there is an optical pickup
comprising a hologram allocated next to the object lens. The light
beam for CD-system is transformed by the hologram from an
infinite-system to a finite-system. It is described in Japanese
Laid-open Patent No. 2003-294926.
[0016] However, because the hologram described in Japanese
Laid-open Patent No. 2003-294926 is a polarization selectable
hologram, it is impossible to use in a polarization light system.
Recently the polarization light system is used in many optical
information recording apparatuses, because the polarization light
system can increase the efficiency of using a light beam. So it is
preferable to use a polarization light system to an optical pickup
corresponding to three kinds of wavelengths (blue-system,
DVD-system and CD-system).
SUMMARY OF THE INVENTION
[0017] An object of the present invention is to solve the above
described problems, and to provide an optical pickup and an optical
information processing apparatus that operate with three kinds of
wavelengths (blue-system, DVD-system and CD-system) with one object
lens to focus on three kinds of optical recording media
(blue-system one, DVD-system one and CD-system one). More
especially, an object of the present invention is to solve the
above described problems, and to provide an optical pickup and an
optical information processing apparatus having a polarization
light system corresponding to three kinds of wavelengths by a
wavelength selectable deflecting element correcting spherical
aberration when the DVD-system medium or CD-system medium is
used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Other objects and further features of the present invention
will become more apparent from the following detailed description
when read in conjunction with the following accompanying
drawings:
[0019] FIG. 1 shows a general configuration of an optical pickup
according to a first embodiment of the present invention;
[0020] FIGS. 2A through 2C show wavefront aberrations focusing on
an optical recording medium according to a first embodiment of the
present invention. FIG. 2A shows when the optical recording medium
is for the blue-system, using a wavelength of 405 nm, NA of 0.67,
.PHI. of 4.0 mm, infinite system incident light beam. FIG. 2B shows
when the optical recording medium is for the DVD-system, using a
wavelength of 660 nm, NA of 0.65, .PHI. of 4.0 mm, infinite system
incident light beam. FIG. 2C shows when the optical recording
medium is for the CD-system, using a wavelength of 785 nm, NA of
0.50, .PHI. of 3.1 mm, infinite system incident light beam;
[0021] FIGS. 3A and 3B show relationships between the object
distance and the wavefront aberration according to a first
embodiment of the present invention. FIG. 3A shows when the light
path is the DVD-system one using an object lens which has an NA of
0.67. FIG. 3B shows when the light path is the CD-system's one
using an object lens which has an NA of 0.67;
[0022] FIGS. 4A through 4D show wavefront aberrations according to
a first embodiment of the present invention. FIG. 4A shows when the
light path is the DVD-system one with finite system or infinite
system using a wavelength of 660 nm, NA of 0.64, .PHI. of 4.0 mm,
and an object distance of 150 mm. FIG. 4B shows when the light path
is the CD-system's one with finite system or infinite system using
a wavelength of 785 nm, NA of 0.48, .PHI. of 3.1 mm, and an object
distance of 50 mm. FIG. 4C shows when the light path is the
DVD-system one with infinite system with aberration correction or
with infinite system without aberration correction using a
wavelength of 660 nm, NA of 0.65, .PHI. of 4.0 mm, and 1st order
deflection. FIG. 4D shows when the light path is the CD-system one
with infinite system with aberration correction or with infinite
system without aberration correction using a wavelength of 785 nm,
NA of 0.50, .PHI. of 3.1 mm, and 1st order deflection;
[0023] FIGS. 5A and 5B show relationships between the object lens
shifts and wavefront aberration according to a first embodiment of
the present invention. FIG. 5A shows when the light path is the
DVD-system one with finite system. FIG. 5B shows when the light
path is the CD-system one with finite system;
[0024] FIGS. 6A through 6C show structures of a wavelength
selectable deflecting element according to a first embodiment of
the present invention. FIG. 6A shows the deflecting area, FIG. 6B
shows a cross-sectional view of an aberration correcting deflecting
area for CD-system, and FIG. 6C shows a cross-sectional view of
limited numerical aperture deflecting area for CD-system;
[0025] FIGS. 7A through 7C show transmission characteristics of
light beam at the wavelength selectable deflecting element with the
aberration correcting deflecting area for CD-system and the limited
numerical aperture deflecting area for CD-system according to a
first embodiment of the present invention. FIG. 7A shows the
transmission characteristics for the blue-system optical recording
medium, FIG. 7B shows the transmission characteristics for the
DVD-system optical recording medium, and FIG. 7C shows the
transmission characteristics for the CD-system optical recording
medium;
[0026] FIGS. 8A through 8C show the relationship between
transmissivity and groove depth of the deflecting pattern for
CD-system according to a first embodiment of the present invention.
FIG. 8A shows the blue-system optical recording medium, FIG. 8B
shows the DVD-system optical recording medium, and FIG. 8C shows
the CD-system optical recording medium;
[0027] FIG. 9 shows specific data for the object lens according to
a first embodiment of the present invention. In this case, the
deflection order for S1 is zero-order for the blue-system light
path, zero-order for the DVD-system light path, and 1st-order for
the CD-system light path. RDY means curvature radius, THI means
thickness, n means refractive index, C1 through C5 at S1 mean
coefficients of deflecting surface, and K, A, B, C and D at S3 and
S4 are coefficients of aspheric lens. The three numbers separated
each word with slash mean for the blue-system light path for first
number, for the DVD-system light path for second number and for the
CD-system light path for third number;
[0028] FIGS. 10A through 10C show a lens shape corresponding to the
specific data shown in FIG. 9. FIG. 10A shows the blue-system
optical recording medium, FIG. 10B shows the DVD-system optical
recording medium, and FIG. 10C shows the CD-system optical
recording medium;
[0029] FIGS. 11A through 11C show transmission characteristics of a
light beam at the wavelength selectable deflecting element with a
limited numerical aperture coating area for CD-system according to
another example of the first embodiment of the present invention.
FIG. 11A shows the transmission characteristics for the blue-system
optical recording medium, FIG. 11B shows the transmission
characteristics for the DVD-system optical recording medium, and
FIG. 11C shows the transmission characteristics for the CD-system
optical recording medium;
[0030] FIG. 12 shows a transmission characteristic of light beam
according to another example of the first embodiment of the present
invention;
[0031] FIG. 13 shows a general configuration of an optical pickup
according to another example of the first embodiment of the present
invention;
[0032] FIG. 14 shows a general configuration of a hologram unit for
a DVD-system and CD-system light path of the optical pickup
described in FIG. 13;
[0033] FIG. 15 shows a coma aberration for the optical pickup of
FIG. 13;
[0034] FIG. 16 shows a general configuration of an optical pickup
according to a second embodiment of the present invention;
[0035] FIGS. 17A through 17C show transmission characteristics of
light beam at the wavelength selectable deflecting element with the
aberration correcting deflecting area for DVD-system according to a
second embodiment of the present invention. FIG. 17A shows the
transmission characteristics for the blue-system optical recording
medium, FIG. 17B shows the transmission characteristics for the
DVD-system optical recording medium, and FIG. 17C shows the
transmission characteristics for the CD-system optical recording
medium;
[0036] FIG. 18 shows the relationship between transmissivity and
groove depth of the deflecting pattern for DVD-system according to
a second embodiment of the present invention;
[0037] FIG. 19 shows specific data for the object lens according to
a second embodiment of the present invention. In this case, the
deflection order for S1 is zero-order for the blue-system light
path, zero-order for the DVD-system light path and 1st-order for
the CD-system light path. The deflection order for S2 is zero-order
for the blue-system light path, 1st-order for the DVD-system light
path and zero-order for the CD-system light path. RDY means
curvature radius, THI means thickness, n means refractive index, C1
through C5 at S1 mean coefficients of deflecting surface, and K, A,
B, C and D at S3 and S4 are coefficients of aspheric lens. The
three numbers separated each word with slash mean for the
blue-system light path for first number, for the DVD-system light
path for second number and for the CD-system light path for third
number;
[0038] FIGS. 20A through 20C show a lens shape corresponding to the
specific data of FIG. 19. FIG. 20A is for the blue-system optical
recording medium, FIG. 20B is for the DVD-system optical recording
medium, and FIG. 20C is for the CD-system optical recording
medium;
[0039] FIGS. 21A through 21C show transmission characteristics of a
light beam at the wavelength selectable deflecting element with an
aberration correcting phase shifter for a DVD-system according to a
second embodiment of the present invention. FIG. 21 A shows the
transmission characteristics for the blue-system optical recording
medium, FIG. 21B shows the transmission characteristics for the
DVD-system optical recording medium, and FIG. 21C shows the
transmission characteristics for the CD-system optical recording
medium;
[0040] FIG. 22A shows a wavefront aberration (shown by a full line)
and a wavefront aberration delayed by phase shift pattern (shown by
a dashed line) according to a second embodiment of the present
invention;
[0041] FIG. 22B shows a wavefront aberration after correction
according to a second embodiment of the present invention;
[0042] FIG. 23 shows a general configuration of an optical pickup
according to a third embodiment of the present invention;
[0043] FIGS. 24A through 24C show transmission characteristics of a
light beam at the wavelength selectable deflecting element with a
limited numerical aperture deflecting area for a DVD-system at
around the aberration correcting deflecting area for DVD-system
according to a third embodiment of the present invention. FIG. 24A
shows the transmission characteristics for the blue-system optical
recording medium, FIG. 24B shows the transmission characteristics
for the DVD-system optical recording medium, and FIG. 24C shows the
transmission characteristics for the CD-system optical recording
medium;
[0044] FIGS. 25A through 25C show wavefront aberrations focusing on
an optical recording medium according to a third embodiment of the
present invention. FIG. 25A shows when the optical recording medium
is the blue-system one using a wavelength of 405 nm, NA of 0.85,
.PHI. of 4.0 mm, and infinite system incident light beam. FIG. 25B
shows when the optical recording medium is the DVD-system one using
a wavelength of 660 nm, NA of 0.65, .PHI. of 3.2 mm, and infinite
system incident light beam. FIG. 25C shows when the optical
recording medium is the CD-system one using a wavelength of 785 nm,
NA of 0.50, .PHI. of 2.5 mm, and infinite system incident light
beam;
[0045] FIGS. 26A and 26B show the relationship between the object
distance and the wavefront aberration according to a third
embodiment of the present invention. FIG. 26A shows when the light
path is the DVD-system one using an object lens which has an NA of
0.85. FIG. 26B shows when the light path is the CD-system one using
an object lens which has an NA of 0.85;
[0046] FIGS. 27A and 27B show wavefront aberrations according to a
third embodiment of the present invention. FIG. 27A shows when the
light path is the DVD-system one with finite system or infinite
system using a wavelength of 660 nm, NA of 0.64, .PHI. of 3.205 mm,
and object distance of 37.5 mm. FIG. 27B shows when the light path
is the CD-system one with finite system or infinite system using
wavelength of 785 nm, NA of 0.47, .PHI. of 3.1 mm, and object
distance of 26 mm;
[0047] FIGS. 28A and 28B show the relationship between the object
lens shifts and the wavefront aberration according to a third
embodiment of the present invention. FIG. 28A shows when the light
path is the DVD-system one with finite system. FIG. 28B shows when
the light path is the CD-system one with finite system;
[0048] FIG. 29 shows specific data for the object lens according to
a third embodiment of the present invention. In this case, the
deflection order for S1 is zero-order for the blue-system light
path, zero-order for the DVD-system light path and 1st-order for
the CD-system light path. The deflection order for S2 is zero-order
for the blue-system light path, 1st-order for the DVD-system light
path and zero-order for the CD-system light path. RDY means
curvature radius, THI means thickness, n means refractive index, C1
through C5 at SI mean coefficients of deflecting surface, and K, A,
B, C and D at S3 and S4 are coefficients of aspheric lens. The
three numbers separated each word with slash mean for the
blue-system light path for first number, for the DVD-system light
path for second number and for the CD-system light path for third
number;
[0049] FIGS. 30A through 30C show a lens shape corresponding to the
specific data shown in FIG. 29. FIG. 30A is for the blue-system
optical recording medium, FIG. 30B is for the DVD-system optical
recording medium, and FIG. 30C is for the CD-system optical
recording medium;
[0050] FIGS. 31A and 31B show wavefront aberrations according to a
third embodiment of the present invention. FIG. 31A shows when the
light path is the DVD-system one with infinite system with
aberration correction or with infinite system without aberration
correction using a wavelength of 660 nm, NA of 0.65, and .PHI. of
3.205 mm. FIG. 31B shows when the light path is the CD-system one
with infinite system with aberration correction or with infinite
system without aberration correction using a wavelength of 785 nm,
NA of 0.51, .PHI. of 2.5 mm;
[0051] FIGS. 32A through 32C show transmission characteristics of
light beam at the wavelength selectable deflecting element with a
limited numerical aperture deflecting area for a DVD-system at
around the aberration correcting deflecting area for a DVD-system
according to another example of the third embodiment of the present
invention. FIG. 32A shows the transmission characteristics for the
blue-system optical recording medium, FIG. 32B shows the
transmission characteristics for the DVD-system optical recording
medium, and FIG. 32C shows the transmission characteristics for the
CD-system optical recording medium;
[0052] FIG. 33 shows a transmission ratio characteristic of
dichroic coating for limiting the numerical aperture coating area
for DVD-system according to the third embodiment of the present
invention; and
[0053] FIG. 34 shows a general configuration of an optical
information processing apparatus according to a fourth embodiment
of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0054] With reference to the accompanying figures, preferred
embodiments of the present invention will now be described.
[0055] FIG. 1 shows a general configuration of an optical pickup
according to a first embodiment of the present invention. By this
optical pickup, information recording, reproduction or deletion is
performed on each of a blue-system optical recording medium, with
an operating wavelength of 405 nm, an NA of 0.67, and a
light-incident side substrate thickness of 0.6 mm; a DVD-system
optical recording medium, with an operating wavelength of 660 nm,
an NA of 0.64, and a light-incident side substrate thickness of 0.6
mm; and a CD-system optical recording medium, with an operating
wavelength of 785 nm, an NA of 0.50 and a light-incident side
substrate thickness of 1.2 mm.
[0056] As shown in FIG. 1, in this optical pickup, a blue-system
through which light with a wavelength of 405 nm passes, includes a
semiconductor laser 101 with a wavelength of 405 nm, a collimator
lens 102, a polarization beam splitter 103, a trichroic prism 104,
a polarization prism 105, a wavelength plate 106, a wavelength
selectable deflecting element 107, an object lens 108, a detection
lens 110, a beam splitting device 111, and a light-receiving device
112.
[0057] Furthermore, a DVD-finite-system through which light with a
wavelength of 660 nm passes includes a hologram unit 201, a
coupling lens 203, a dichroic prism 205, the trichroic prism 104,
the polarization prism 105, the wavelength plate 106, the
wavelength selectable deflecting element 107, and the object lens
108.
[0058] A CD optical system through which light with a wavelength of
785 nm passes includes a hologram unit 211, a coupling lens 212,
the dichroic prism 205, the trichroic prism 104, the polarization
prism 105, the wavelength plate 106, the wavelength selectable
deflecting element 107, and the object lens 108.
[0059] That is, the dichroic prism 205, the trichroic prism 104,
the polarization prism 105, the wavelength plate 106, the
wavelength selectable deflecting element 107, and the object lens
108 are common parts for the above-mentioned two or three optical
systems.
[0060] The object lens 108 is designed so that the spherical
aberration occurring when an infinite system is applied is minimum,
especially for a blue-system optical recording medium with an
operating wavelength of 405 nm, an NA of 0.67, and a light-incident
side substrate thickness of 0.6 mm.
[0061] The object lens 108 and the wavelength selectable deflecting
element 107 are on an actuator 108b, and are able to move in the
focusing direction and the tracking direction.
[0062] As for optical recording media 109a, 109b, and 109c to be
loaded, these optical recording media have substrate thicknesses
and operating wavelengths different from each other. Specifically,
the blue-system optical recording medium 109a has a substrate
thickness of 0.6 mm; the DVD-system optical recording medium 109b
has a substrate thickness of 0.6 mm; and the CD-system optical
recording medium 109c has a substrate thickness of 1.2 mm. During
information recording or reproduction, on a rotation mechanism not
shown, one optical recording medium thereof is loaded, and, is
thereby rotated at high speed.
[0063] In the above-described optical pickup, a case where
information recording, reproduction or deletion is performed on the
blue-system optical recording medium, with an operating wavelength
of 405 nm, an NA of 0.67, and a light-incident side substrate
thickness of 0.6 mm will now be described. A beam emitted in a
linear polarization from the semiconductor laser 101 with a
wavelength of 405 nm is transformed into an approximately parallel
beam by the collimator lens 102, and then, passes through the
polarization beam splitter 103 and the trichroic prism 104. After
that, the light path is deflected 90 degrees by the polarization
prism 105, and the beam then passes through the wavelength plate
106, by which it is transformed into a circular polarization. After
that, the beam then passes through the wavelength selectable
deflecting element 107, no effect is provided at all, and then it
is incident on the object lens 108, by which it is focused into a
minute spot on the optical recording medium 109a. Informational
recording, reproduction, or deletion is performed by this spot on
the optical recording medium.
[0064] After being reflected by the optical recording medium 109a,
the light has a circular polarization in the direction opposite to
that in the above-mentioned case of coming into the optical
recording medium. The light is transformed into an approximately
parallel beam again, is transformed into a linear polarization
perpendicular to that in the above-mentioned case of coming into
the optical recording medium by the wavelength plate 106, and is
reflected by the polarization beam splitter 103, converged by the
detection lens 110, and deflected in a splitting manner by the beam
splitting device 111 into a plurality of beams, which are then
incident on the light-receiving device 112. From the
light-receiving device 112, an aberration signal, an information
signal, and a servo signal are detected.
[0065] Next, a case will now be described involving information
recording, reproduction or deletion on the DVD-system optical
recording medium with the operating wavelength of 660 nm, an NA of
0.65, and a light-incident side substrate thickness of 0.6 mm. As
mentioned above, light receiving/emitting devices are installed in
a pickup for a DVD system into one unit, and such a hologram unit
which separates an incident beam using a hologram is generally
used, and, as such, the hologram unit 201 shown in FIG. 1
integrally includes a semiconductor laser 201 a, a hologram 201b,
and a light-receiving device 201c. The 660 nm light which comes out
of the semiconductor laser 201a of the hologram unit 201 passes
through the hologram 201b and thus, is transformed into a
predetermined unparallel beam by the coupling lens 203. Then, the
beam is transmitted through the dichroic prism 205, which transmits
light in a red wavelength zone while it reflects light in an
infrared wavelength zone. The beam is reflected by the trichroic
prism 104 which transmits light in a blue wavelength zone while it
reflects light in a red wavelength zone, in the direction toward
the polarization prism 105. The polarization prism 105 deflects the
light path 90 degrees, and the wavelength plate 106 then transforms
the beam into a circular or elliptic polarization, and with the
wavelength selectable deflecting element 107, no effect is provided
at all, and the beam then is incident on the object lens 108, by
which the beam is focused into a minute spot on the optical
recording medium 109b. Informational recording, reproduction, or
deletion is performed by this spot on the optical recording
medium.
[0066] After being reflected by the optical recording medium 109b,
the beam is reflected by the polarization prism 105, reflected by
the trichroic prism 104, converged by the coupling lens 203, and
diffracted by the hologram 201b in the direction toward the
light-receiving device 201c, which is held in the same unit as the
semiconductor laser 201a. From the light-receiving device 201c, an
aberration signal, an information signal, and a servo signal are
detected.
[0067] A case will now be described where information recording,
reproduction, or deletion is performed on the CD-system optical
recording medium with an operating wavelength of 785 nm, an NA of
0.50, and a light-incident side substrate thickness of 1.2 mm. As
in the above-described case for a DVD system, a pickup of CD system
also has light receiving/emitting devices in one unit, and, a
hologram unit which separates beams using a hologram is used
generally. As such, the hologram unit 211 shown in FIG. 1
integrally includes a semiconductor laser 211a, a hologram 211b,
and a light-receiving device 211c, as in the hologram unit 201. A
785 nm light, which comes out of the semiconductor laser 211a of
the hologram unit 211, passes through the hologram 211b, and is
made into a parallel light by the collimator lens 212. After that,
this light is reflected by the dichroic prism 205 which transmits
light in the red wavelength zones while it reflects each of lights
in the blue and infrared wavelength zones, and is reflected by the
trichroic prism 104 which transmits light in the blue wavelength
zone while it reflects each of lights in the red and infrared
wavelength zones, in the direction toward the polarization prism
105. The polarization prism 105 deflects the light path 90 degrees.
The wavelength plate 106 transforms the light into an elliptic
polarization or a circular polarization, and the light is
controlled in its cross section into NA: 0.50 with the wavelength
selectable deflecting element 107. The beam is deflected for 1st
order by the wavelength selectable deflecting element 107 to make a
minute spot. After that, the light is incident on the object lens
108, and thereby, it is focused into a minute spot on the optical
recording medium 109c. Informational recording, reproduction, or
deletion is performed by this spot on the optical recording medium
109c.
[0068] After being reflected by the optical recording medium 109c,
the light is deflected by the polarization prism 105, reflected by
the trichroic prism 104, reflected by the dichroic prism 205,
converged by the collimator lens 212, and diffracted by the
hologram 211b in the direction toward the light-receiving device
211c, which is held in the same unit as the semiconductor laser
211a. From the light-receiving device 211c, an aberration signal,
an information signal, and a servo signal are detected. From
light-receiving device 211c, an aberration signal, an information
signal, and a servo signal are detected.
[0069] Next, a case will be described where the wavelength
selectable deflecting element is used for compatibility with the
blue-system, operating wavelength of 660 nm and NA: 0.65,
DVD-system and CD-system.
[0070] FIG. 2A shows when the optical recording medium is for the
blue-system, with a wavelength of 405 nm, an NA of 0.67, .delta. of
4.0 mm, infinite system incident light beam. FIG. 2B shows when the
optical recording medium is for the DVD-system, with a wavelength
of 660 nm, NA of 0.65, .PHI. of 4.0 mm, infinite system incident
light beam. FIG. 2C shows when the optical recording medium is for
the CD-system, with a wavelength of 785 nm, NA of 0.50, .delta. of
3.1 mm, infinite system incident light beam.
[0071] The single object lens 108 has optimum aberration
characteristics at a wavelength of 405 nm and a substrate thickness
of 0.6 mm (as shown in FIG. 2A). When light with a wavelength of
660 nm, in an infinite system, is incident on the single object
lens 108, a beam spot is formed on the DVD-system optical
recording-medium 109b, with a substrate thickness 0.6 mm, and the
wavefront aberration is shown in FIG. 2B. The horizontal axis of
FIG. 2B represents a pupil radius position and the vertical axis of
FIG. 2B represents wavefront aberration. FIG. 2B shows a two
dimensional cross-sectional shape of phase differential
distribution, but actually, there is a three dimensional
distribution and it has rotational symmetry around the vertical
axis. The DVD-system light path according to a first embodiment of
the present invention has a finite-system to correct the
aberration. FIG. 3A shows the relationship between the object
distance and the wavefront aberration when the light path is the
DVD-system one using an object lens which has an NA of 0.67. The
wavefront aberration is minimum around the object distance of 150
mm. FIG. 4A shows a wavefront aberration when the light path is the
DVD-system one with a finite or infinite system using a wavelength
of 660 nm, NA of 0.64, .PHI. of 4.0 mm and object distance of 150
mm.
[0072] Same as above, when light with a wavelength of 785 nm is
incident on the single object lens 108, with an infinite system, a
beam spot is formed on the CD-system optical recording-medium 109c,
which has a substrate thickness of 1.2 mm, and the wavefront
aberration is shown in FIG. 2C. The horizontal axis of FIG. 2C
represents a pupil radius position and the vertical axis of FIG. 2C
represents a wavefront aberration. FIG. 3B shows the relationship
between the object distance and the wavefront aberration when the
light path is the CD-system one using an object lens which has an
NA of 0.50. The wavefront aberration is minimum around the object
distance of 50 mm. But the object distance at the minimum wavefront
aberration is shorter than the DVD-system one. As above described,
there is a problem from the effect of the object lens shifts. FIGS.
5A and 5B show relationships between the object lens shifts and the
wavefront aberration. FIG. 5A shows when the light path is the
DVD-system one with finite system. FIG. 5B shows when the light
path is the CD-system one with finite system. It is preferable that
the object lens shift is 0.3 mm to 0.4 mm, but especially, the
deterioration in the CD-system is close to Marecial's criterion of
0.07 .lamda.rms, which is an upper limitation of wavefront
aberration generally.
[0073] As above described, it is preferable to use the
infinite-system in the CD-system. In a first embodiment of the
invention, the spherical aberration at incident with
infinite-system is corrected by the wavelength selectable
deflecting element 107.
[0074] The wavelength selectable deflecting element 107 of the
first embodiment of this invention is not the same as the
deflecting element described in Japanese Patent No. 3240846. The
wavelength selectable deflecting element 107 has a wavelength
selectable deflecting area. Therefore, it becomes possible to use a
polarization light system. Generally, a polarization selectable
deflecting element has a complicated structure, for example, a
sandwich of isotropic material and birefringence material between
glass substrates. But a wavelength selectable deflecting element
has a simple structure, for example, with a deflect surface on
glass or plastic substrate. The deflecting area may be a plural
ring with a center on the incident light beam axis as shown in FIG.
6A. The cross-section of the deflecting area may have a rectangular
shape as shown in FIG. 6B. There are methods for making the deflect
area, for example, use photolithography technology, or precision
cutting by diamond turning tool.
[0075] The aberration correcting deflecting area for CD-system 107a
emits a zero-order deflected light beam when the incoming light
beam has a wavelength of 405 nm as shown in FIG. 7A. In other
words, for a light beam having a wavelength of 405 nm, the
aberration correcting deflecting area for CD-system 107a provides
no effect at all. The zero-order deflected light beam is focused
onto the blue-system optical recording medium 109a by the object
lens 108. The aberration correcting deflecting area for CD-system
107a also emits a zero-order deflected light beam when a light beam
having a wavelength of 660 nm is incoming as shown in FIG. 7B. In
other words, for a light beam having a wavelength of 660 nM, the
aberration correcting deflecting area for CD-system 107a provides
no effect at all. The zero-order deflected light beam is focused
onto the DVD-system optical recording medium 109b by the object
lens 108. On the other hand, the aberration correcting deflecting
area for CD-system 107a emits 1st-order deflected light beam when a
light beam having a wavelength of 785 nm is incoming as shown in
FIG. 7C. As above described, the aberration correcting deflecting
area for CD-system 107a transmits a light beam in a blue wavelength
zone and also transmits a light beam in a red wavelength zone. But
the aberration correcting deflecting area for CD-system 107a
deflects a light beam in an infrared wavelength zone.
[0076] The deflecting ratio is designed to correct the spherical
aberration in the object lens for the light beam having a
wavelength of 785 nm and the spherical aberration in the substrate
of the CD-system optical recording medium 109c for the light beam
having a wavelength of 785 nm. As such, it becomes possible to
focus the light beam having a wavelength of 785 nm onto the
CD-system optical recording medium 109c. FIG. 4D shows a wavefront
aberration when the light path is the CD-system one with infinite
system with aberration correction or with infinite system without
aberration correction, using a wavelength of 785 nm, an NA of 0.50,
.delta. of 3.1 mm, and 1st order deflection.
[0077] FIG. 6B is a cross-sectional view of an aberration
correcting deflecting area for a CD-system wavelength selectable
deflecting element. Because a phase difference of frequently
concave and convex shape at the cross-section is to be 2.pi. times
of 405 nm and 660 nm, it becomes possible to have zero-order
transmissivity for the light beam having a wavelength of 405 nm and
660 nm and have 1st-order diffraction efficiency for the light beam
having a wavelength of 785 nm. FIGS. 8A through 8C show the
relationship between transmissivity and groove depth of the
deflecting pattern for the CD-system. FIG. 8A shows the blue-system
optical recording medium, FIG. 8B shows the DVD-system optical
recording medium, and FIG. 8C shows the CD-system optical recording
medium. The zero-order transmissivity for the light beam having a
wavelength of 405 nm and 660 nm becomes almost 100% around the
groove depth of 3.8 .mu.m. The 1st-order diffraction efficiency for
the light beam having a wavelength of 785 nm becomes almost 100%
around the groove depth of 3.8 .mu.m. Because it is easy to make a
shallow groove, the groove depth should preferably be the least
common multiple of 405 nm and 660 nm.
[0078] Next, specific data for the shape of the object lens and the
wavelength selectable deflecting element will be provided.
[0079] An aspheric shape of a lens surface is defined by the
following formula:
X=(Y.sup.2/R)/[1+ {1-(1++K)
Y/R.sup.2}+AY.sup.4+BY.sup.6+CY.sup.8+DY.sup.10+EY.sup.12+FY.sup.14+
. . . ]
[0080] where
[0081] X denotes the coordinate along the optical axis direction; Y
denotes the coordinate along the direction perpendicular to the
optical axis; R denotes the paraxial curvature radius; K denotes
the cone constant; A, B, C, D, E, F . . . denote high-order
coefficients, shown in the table of lens data of FIG. 9.
[0082] The phase function of a deflecting element is defined by the
following formula:
.PHI.(r)=m(2.pi./.lamda.) (C1+C2 r.sup.2+C3 r.sup.4+C4 r.sup.6+C5
r.sup.8+ . . . )
[0083] where
[0084] m denotes the deflection order; .lamda. denotes the
wavelength; r denotes the radius from the optical axis; C1, C2, C3,
C4, C5, . . . denote coefficients, shown in the table of lens data
of FIG. 9.
[0085] The object lens according to a first embodiment of this
invention has an operating wavelength of 405 nm; NA of 0.67; f of
3.00 mm; and n of 1.59; vd of 61.3, shown in the table of lens data
of FIG. 9. In FIG. 9, "OBJ" represents the object point (laser
diode used for optical source). Because the object lens 108 forms
the infinite-system for the wavelength of 405 nm and 785 nm,
"INFINITY" for the curvature radius RDY and the thickness THI means
that the optical source is located at the infinite distance. On the
other hand, the DVD-system is finite-system and the object distance
is 150 mm. Here, all the quantities having the dimension of length
are represented by "mm".
[0086] SI represents a surface of the wavelength selectable
deflecting element 107 at the side of the optical source, S2
represents a surface of the wavelength selectable deflecting
element 107 at the side of the optical recording medium, S3
represents the lens surface of the object lens 108 at the side of
the optical source, S4 represents the lens surface of the object
lens 108 at the side corresponding to the optical recording medium.
The objective lens 108 has a thickness of 1.70 mm, and the
thickness value "1.64 mm" for THI in the column for S4 represents
the "working distance." Further, S5 represents the surface of the
optical recording medium 109 irradiated with the optical beam and
hence located at the side of the optical source, S6 represents the
opposite side surface of the optical recording medium 109 (at the
side of the optical source). The distance between S5 and S6 (the
substrate thickness) is 0.6 mm for the blue-system optical
recording medium, 0.6 mm for the DVD-system optical recording
medium, and 1.2 mm for the CD-system optical recording medium. EPD
represents an incident pupil diameter. EPD is 4.0 mm for the
blue-system and the DVD-system, and 3.1 mm for the CD-system. WL
represents the wavelength.
[0087] The wavefront aberration in the optical system using the
above described object lens and wavelength selectable deflecting
element is 0.0020 .lamda.rms for the blue-system, 0.0371 .lamda.rms
for the DVD-system, and 0.0001 .lamda.rms for the CD-system using a
1st-order deflecting light beam. They are under the Marecial's
criterion of 0.07 .lamda.rms. FIGS. 10A through 10C show a lens
shape corresponding to the specific data of FIG. 9. FIG. 10A is for
the blue-system optical recording medium, FIG. 10B is for the
DVD-system optical recording medium, and FIG. 10C is for the
CD-system optical recording medium.
[0088] In FIG. 7, the aberration correcting deflecting area for
CD-system 107a is located at the light source side of the
wavelength selectable deflecting element 107, but it may be located
at the side of the optical recording medium. Also the aberration
correcting deflecting area for the CD-system 107a may be on the
object lens. These are the same as in other embodiments.
[0089] Next, a case will now be described a condition related with
the NA and the light beam diameter. It is necessary to switch the
numerical aperture (NA) value according to the optical recording
medium. Therefore, NA is 0.67 for the blue-system optical recording
medium, 0.64 for the DVD-system optical recording medium, and 0.50
for the CD-system optical recording medium.
[0090] The NA is defined by the following formula:
NA(.lamda.)=.PHI.(.lamda.)/2/f(.lamda.)
[0091] where
[0092] f denotes the focal distance of the object lens; and .PHI.
denotes an effective diameter of the light beam used for
focusing.
[0093] According to the above described, because the focal
distances for the blue-system and the DVD-system are 3.00 and 3.10
mm, respectively, the NA almost satisfies the recommended DVD and
HD-DVD standards when .PHI. is 4.00 mm.
[0094] Generally, because the focal distance is longer when the
wavelength is longer, it is preferable to choose the effective
diameter for the NA a little bit lower from 0.65 for the
DVD-system, and an NA a little bit higher from 0.65 for the
blue-system. However, because the focal distance for the CD-system
is 3.12 mm, it is necessary to use a numerical aperture switching
means to obtain an NA of 0.5. To solve this problem, in this
embodiment, there is a wavelength selectable numerical aperture
limiting area for switching the light beam diameter by reflecting
or deflecting corresponding to wavelength.
[0095] As above described, it is necessary to switch the numerical
aperture for wavelengths of 405 nm and 660 nm and for a wavelength
of 785 nm. To switch the numerical aperture, the light beam is
limited by an aperture 108c in an actuator 108b for wavelengths of
405 nm and 660 nm as shown in FIG. 7A, FIG. 7B and FIG. 7C. And
also to switch the numerical aperture, the light beam is limited by
a numerical aperture limiting deflecting area for the CD-system
107b. It is located around the aberration correcting deflecting
area for the CD-system 107a, to switch the light beam diameter
corresponding to the wavelength of the light beam emitted from the
light source for wavelength of 785 nm as shown in FIG. 7C. FIG. 7A
shows the transmission characteristics for the blue-system optical
recording medium, FIG. 7B shows the transmission characteristics
for the DVD-system optical recording medium, and FIG. 7C shows the
transmission characteristics for the CD-system optical recording
medium. The numerical aperture limiting deflecting area for the
CD-system 107b transmits a light beam in a blue wavelength zone and
also transmits a light beam in a red wavelength zone. But the
numerical aperture limiting deflecting area 107b deflects a light
beam in an infrared wavelength zone for 1st-order deflecting light
beam.
[0096] FIG. 6C is a cross-sectional view of the deflecting pattern
of the numerical aperture limiting deflecting area 107b. Because a
phase difference of frequently concave and convex cross-section is
to be 2.pi. times of 405 nm and 660 nm, it becomes possible to
reduce a 1st-order diffraction efficiency for the light beam having
wavelength of 405 nm and 660 nm and have a 1st-order diffraction
efficiency for the light beam having a wavelength of 785 nm the
same as the aberration correcting deflecting area for CD-system
shown in FIG. 6B and FIG. 7.
[0097] A light beam emitted from the light source and deflected by
the numerical aperture limiting deflecting area for CD-system 107b
is scattered to avoid overlapping with the focused light spot.
[0098] And as to the other example of a first embodiment, a
transmission and reflection switching means may be used instead of
the numerical aperture limiting deflecting area for CD-system 107b,
as shown in FIG. 11. Therefore, it may have a limiting numerical
aperture coating area 107c evaporated a dichroic coating around the
aberration correcting deflecting area for CD-system 107a to switch
the light beam diameter by transmission and reflection as shown in
FIG. 12. So, it becomes possible to transmit the light beam having
a wavelength of 405 nm and 660 nm and reflect the light beam having
a wavelength of 785 nm as shown in FIG. 11A, FIG. 11B and FIG. 11C.
The wavelength selectable deflecting element 107 is slanted so that
the reflected light beam having a wavelength of 785 nm is not
incident on a photo detector.
[0099] FIG. 13 shows a general configuration of an optical pickup
according to another example of the first embodiment of the present
invention. There is a hologram unit 211 including a light source
for a DVD-system and a light source for a CD-system in one package.
In this case, it is possible to minimize the optical pickup.
However, because it is necessary that the light sources for the
DVD-system and the CD-system, in the hologram unit 211, be
separated by at least several hundred .mu.m, it is impossible to
set the light sources on the same light axis, as shown in FIG. 14.
Therefore, a coma aberration occurs as shown in FIG. 15. In this
case, it is possible to obtain a good spot when a deflecting
pattern to reduce the coma aberration is overlapped.
[0100] FIG. 16 shows a general configuration of an optical pickup
according to a second embodiment of the present invention. By this
optical pickup, information recording, reproduction or deletion is
performed on each of a blue-system optical recording medium, with
an operating wavelength of 405 nm, an NA of 0.67, and a
light-incident side substrate thickness of 0.6 mm; a DVD-system
optical recording medium, with an operating wavelength of 660 nm,
an NA of 0.64, and a light-incident side substrate thickness of 0.6
mm; and a CD-system optical recording medium, with an operating
wavelength of 785 nm, an NA of 0.50 and a light-incident side
substrate thickness of 1.2 mm. The optical pickup has an
infinite-system for the DVD-system. In this case, it is possible to
increase the optical system layout freedom.
[0101] In the above-described optical pickup, a case where
information recording, reproduction or deletion is performed on the
blue-system optical recording medium, with the operating wavelength
of 405 nm, an NA of 0.67, and a light-incident side substrate
thickness of 0.6 mm, will now be described. A linearly polarized
beam emitted from the semiconductor laser 101 with a wavelength of
405 nm is transformed into an approximately parallel beam by the
collimator lens 102, and then, passes through the polarization beam
splitter 103 and the trichroic prism 104. After that, the light
path is deflected 90 degrees by the polarization prism 105, and the
beam then passes through the wavelength plate 106, by which it is
transformed into a circular polarization. And after that, the beam
then passes through the wavelength selectable deflecting element
107, no effect is provided at all, and then it is incident on the
object lens 108, by which it is focused into a minute spot on the
optical recording medium 109a. Informational recording,
reproduction, or deletion is performed by this spot on the optical
recording medium.
[0102] After being reflected by the optical recording medium 109a,
the light has a circular polarization in the direction opposite to
that in the above-mentioned case of coming into the optical
recording medium, is transformed into an approximately parallel
beam again, is transformed into a linear polarization perpendicular
to that in the above-mentioned case of coming into the optical
recording medium by the wavelength plate 106, and is reflected by
the polarization beam splitter 103, converged by the detection lens
110, and deflected in a splitting manner by the beam splitting
device 111 into a plurality of beams, which are then incident on
the light-receiving device 112. From the light-receiving device
112, an aberration signal, an information signal, and a servo
signal are detected.
[0103] Next, a case will now be described where information
recording, reproduction or deletion is performed on the DVD-system
optical recording medium, with the operating wavelength of 660 nm,
an NA of 0.65, and a light-incident side substrate thickness of 0.6
mm. The hologram unit 201 integrally includes a semiconductor laser
201a, hologram 201b, and light-receiving device 201c. The 660 nm
light which comes out of the semiconductor laser 201a passes
through the hologram 201b and thus, is transformed into an
approximately parallel beam by the collimator lens 202. Then, the
beam is transmitted through the dichroic prism 205 which transmits
light in a red wavelength zone while it reflects light in an
infrared wavelength zone, and is reflected by the trichroic prism
104 which transmits light in a blue wavelength zone while it
reflects light in a red wavelength zone, in the direction toward
the polarization prism 105. The light path is deflected 90 degrees
by the polarization prism 105, and the wavelength plate 106 then
transforms the beam into a circular or elliptic polarization. The
beam is deflected for 1st order by the wavelength selectable
deflecting element 107 to make a minute spot, and the beam then is
incident on the object lens 108, by which the beam is focused into
a minute spot on the optical recording medium 109b. Informational
recording, reproduction, or deletion is performed by this spot on
the optical recording medium.
[0104] After being reflected by the optical recording medium 109b,
the beam is reflected by the polarization prism 105, reflected by
the trichroic prism 104, converged by the collimator lens 202, and
diffracted by the hologram 201b in the direction toward the
light-receiving device 201c, which is in the same package as the
semiconductor laser 201a. From the light-receiving device 201c, an
aberration signal, an information signal, and a servo signal are
detected.
[0105] A case will now be described where information recording,
reproduction, or deletion is performed on the CD-system optical
recording medium, with an operating wavelength of 785 nm, an NA of
0.50, and a light-incident side substrate thickness of 1.2 mm. As
in the above-described case for a DVD system, a CD system pickup
also has light receiving/emitting devices in one package or unit,
and, a hologram unit which separates beams using a hologram is used
generally. As such, the hologram unit 211 integrally includes a
semiconductor laser 211a, a hologram 211b, and a light-receiving
device 211c, as in the hologram unit 201. 785 nm light emitted by
the semiconductor laser 211a passes through the hologram 211b, and
is made into a parallel light beam by the collimator lens 212.
After that, the light is reflected by the dichroic prism 205 which
transmits light in the red wavelength zones while it reflects
lights in the blue and infrared wavelength zones, and is reflected
by the trichroic prism 104 which transmits light in the blue
wavelength zone while it reflects lights in the red and infrared
wavelength zones, in the direction toward the polarization prism
105. The light path is deflected 90 degrees by the polarization
prism 105. The wavelength plate 106 transforms the light into an
elliptic polarization or a circular polarization, and the light is
controlled in its cross section to an NA of 0.50 by the wavelength
selectable deflecting element 107. The beam is deflected for 1st
order by the wavelength selectable deflecting element 107 to make a
minute spot. After that, the light is incident on the object lens
108, and thereby, it is focused into a minute spot on the optical
recording medium 109c. Informational recording, reproduction, or
deletion is performed by this spot on the optical recording medium
109c.
[0106] After being reflected by the optical recording medium 109c,
the light is deflected by the polarization prism 105, reflected by
the trichroic prism 104, reflected by the dichroic prism 205,
converged by the collimator lens 212, and diffracted by the
hologram 211b in the direction toward the light-receiving device
211c, which is held in the same package or unit as the
semiconductor laser 211a. From the light-receiving device 211c, an
aberration signal, an information signal, and a servo signal are
detected.
[0107] Next, a case will now be described where a wavelength
selectable deflecting element is used for compatibility with the
blue-system, operating wavelength of 660 nm and NA of 0.65,
DVD-system and CD-system. Because the numerical aperture limiting
deflecting area for the CD-system 107b in this embodiment is the
same as the numerical aperture limiting deflecting area 107b in the
first embodiment, a description of the deflecting area 107b is
omitted. An aberration correcting deflecting area for DVD-system
107d, which is different from the detailed description of the first
preferred embodiment, will now be described.
[0108] It was already described above that the aberration
characteristic for the single object lens 108 is optimum at the
wavelength of 405 nm and the substrate thickness of 0.6 mm. When
light with a wavelength of 660 nm is incident on the lens 108, with
an infinite system, a beam spot is formed on the DVD-system optical
recording-medium 109b (substrate thickness of 0.6 mm) and the
wavefront aberration is as shown in FIG. 2B.
[0109] As an aberration correction area for DVD-system, it is
preferable that a diffraction pattern is designed to transmit light
in a blue wavelength zone and light in a red wavelength zone, no
effect is provided at all, and deflect to correct the spherical
aberration. It is known, as described in Japanese Laid-open Patent
No. 2003-177226, to reduce such a spherical aberration by a
deflecting area. Referring now to FIG. 17A, FIG. 17B and FIG. 17C,
the aberration correcting deflecting area for DVD-system 107d has a
4 level stair-step shaped section for example. The aberration
correcting deflecting area for DVD-system 107d emits a zero-order
deflected light beam when light in a blue wavelength zone and light
in a red wavelength zone is incoming. The aberration correcting
deflecting area for DVD-system 107d emits a 1st-order deflected
light beam when light in a blue wavelength zone and light in an
infrared wavelength zone is incoming. Therefore, as above
described, the aberration correcting deflecting area for DVD-system
107d transmits a light beam in a blue wavelength zone and also
transmits a light beam in a red wavelength zone. But the aberration
correcting deflecting area 107d deflects a light beam in an
infrared wavelength zone. The deflecting ratio is designed to
correct the spherical aberration in the object lens 108 for the
light beam having a wavelength of 660 nm and the spherical
aberration in the substrate of the DVD-system optical recording
medium 109b for the light beam having a wavelength of 660 nm. As
such, it becomes possible to focus the light beam having a
wavelength of 660 nm onto the DVD-system optical recording medium
109b.
[0110] The aberration correcting deflecting area for DVD-system
107d does not have a rectangular shape but rather has a 4 level
stair-step shaped section. In this case, a zero-order deflecting
light transmissivity .eta..sub.0, the +1st-order deflecting light
deflection efficiency .eta..sub.+1 and the -1st-order deflecting
light deflection efficiency .eta..sub.-1 are defined by the
following formulas:
.eta..sub.0=cos.sup.2(.PHI./2)cos.sup.4(.PHI./4)
.eta..sub.+1=(8/.pi..sup.2)sin.sup.2(.PHI./2)cos.sup.2[(.PHI.-.pi.)/4]
.eta..sub.-1=(8/.pi..sup.2)sin.sup.2(.PHI./2)cos.sup.2[(.PHI.+.pi.)/4]
(.PHI.=2.pi.(n-1)h/.lamda.)
[0111] where
[0112] h denotes the height of each stair-step; n denotes the
refractive index; .lamda. denotes the wavelength of incident
light.
[0113] FIG. 18 shows the relationship between transmissivity and
groove depth of the deflecting pattern for DVD-system. For example,
under the conditions h of 1.53 .mu.m, the height of 4 stair-steps
of 4.58 .mu.m, materials of BK7 (manufactured by HOYA), .lamda. of
405 nm and n of 1.530, because .PHI. is 12.pi., the zero-order
deflecting light transmissivity .eta..sub.0 becomes 1, the
+1st-order deflecting light deflection efficiency .eta..sub.+1
becomes 0, and the -1st-order deflecting light deflection
efficiency .eta..sub.-1 becomes 0. And for example, under the
conditions h of 1.53 .mu.m, the height of 4 stair-steps of 4.58
.mu.m, materials of BK7 (manufactured by HOYA), .lamda. of 660 nm
and n of 1.514, because .PHI. is 7.13.pi., the zero-order
deflecting light transmissivity .eta..sub.0 becomes 1, the
+1st-order deflecting light deflection efficiency .eta..sub.30 1
becomes 0.01, and the -1st-order deflecting light deflection
efficiency .eta..sub.-1 becomes 0.76. And also for example, under
the conditions h of 1.53 .mu.m, the height of 4 stair-steps of 4.58
.mu.m, materials of BK7 (manufactured by HOYA), .lamda. of 785 nm
and n of 1.5111, because .PHI. is 4.pi., the zero-order deflecting
light transmissivity .eta..sub.0 becomes 1, the +1st-order
deflecting light deflection efficiency .eta..sub.+1 becomes 0, and
the -1st-order deflecting light deflection efficiency .eta..sub.-1
becomes 0. As above described, .eta..sub.0.sup.2 becomes 1 for
.lamda. of 405 nm, .eta..sub.0.sup.2 becomes 1 for .lamda. of 660
nm, and .eta..sub.0.sup.2 becomes 0.58 for .lamda. of 785 nm.
[0114] Next, referring to FIG. 19, specific data is provided for
the object lens according to the second embodiment of the present
invention. As shown in FIG. 17, the aberration correcting
deflecting area for CD-system 107a and the numerical aperture
limiting deflecting area for CD-system 107b are located at the
light source side of the wavelength selectable deflecting element
107, and the aberration correcting deflecting area for DVD-system
107d is located at the object lens side of the wavelength
selectable deflecting element 107. In FIG. 19, "OBJ" represents the
object point (laser diode used for optical source). Because the
object lens 108 forms the infinite-system for wavelengths of 405
nm, 660 nm and 785 nm, "INFINITY" for the curvature radius RDY and
the thickness THI means that the optical source is located at the
infinite distance. Here, all the quantities having the dimension of
length are represented by "mm."
[0115] S1 represents a surface of the wavelength selectable
deflecting element 107 at the side of the optical source, S2
represents a surface of the wavelength selectable deflecting
element 107 at the side of the optical recording medium, S3
represents the lens surface of the object lens 108 at the side of
the optical source, S4 represents the lens surface of the object
lens 108 at the side of the optical recording medium. The objective
lens 108 has a thickness of 1.70 mm, and the thickness value "1.64
mm" at the THI in the column for S4 represents the "working
distance." Further, S5 represents the surface of the optical
recording medium 109 irradiated by the optical beam and hence
located at the side of the optical source, S6 represents an
opposite side of the surface of the optical recording medium 109
irradiated with the optical beam and hence located at the side of
the optical source. The distance between S5 and S6 (the substrate
thickness) is 0.6 mm for the blue-system optical recording medium,
0.6 mm for the DVD-system optical recording medium, and 1.2 mm for
the CD-system optical recording medium. EPD represents an incident
pupil diameter. EPD is 4.0 mm for the blue-system, 4.0 mm for the
DVD-system, and 3.1 mm for the CD-system. WL represents the
wavelength. FIGS. 20A through 20C show a lens shape corresponding
to the specific data of FIG. 19. FIG. 20A shows the blue-system
optical recording medium, FIG. 20B shows the DVD-system optical
recording medium, and FIG. 20C shows the CD-system optical
recording medium.
[0116] The wavefront aberration in the above-described optical
system is 0.0020 .lamda.rms for the blue-system, 0.0020 .lamda.rms
for the DVD-system, and 0.0001 .lamda.rms for the CD-system. They
are under the Marecial's criterion of 0.07 .lamda.rms.
[0117] In the above described case, the aberration correcting
deflecting area for the CD-system 107a and the numerical aperture
limiting deflecting area for the CD-system 107b are located at the
light source side of the wavelength selectable deflecting element
107. The aberration correcting deflecting area for DVD-system 107d
is located at the object lens side of the wavelength selectable
deflecting element 107, but it may be located on the opposite side.
And also in whole or in part of the aberration correcting
deflecting area for CD-system 107a, the numerical aperture limiting
deflecting area for CD-system 107b and the aberration correcting
deflecting area for DVD-system 107d may be made on the object
lens.
[0118] Next, another example of the second embodiment of the
invention will be described. FIGS. 21A through 21C show
transmission characteristics of a light beam at the wavelength
selectable deflecting element with an aberration correcting phase
shifter for DVD-system. FIG. 21A shows the transmission
characteristics for the blue-system optical recording medium, FIG.
21B shows the transmission characteristics for the DVD-system
optical recording medium, and FIG. 21C shows the transmission
characteristics for the CD-system optical recording medium. It may
be used instead of the above described aberration correction
element, as shown in FIG. 21.
[0119] A shift pattern of an aberration correction phase shifter
area for DVD-system 107e on the wavelength selectable deflecting
element 107 provides no effect at the wavelength of 405 nm and the
wavelength of 785 nm. But the shift pattern of the aberration
correction phase shifter area for CD-system 107e on the wavelength
selectable deflecting element 107 provides maximum effect for the
wavelength of 660 nm.
[0120] It is possible to provide no effect in the wavelength of 405
nm and the wavelength of 785 nm by satisfying the following
formula:
.delta.(.lamda.)=2.pi.(n-1)h/.lamda.
[0121] where
[0122] h denotes the height of each stair-step; and .lamda. denotes
the wavelength of incident light.
[0123] In the above described case, it is preferable to choose the
phase difference .delta. (405 nm) and .delta. (785 nm) to be 2.pi.
times an integral number. The phase difference .delta. is defined
by the substrate materials. For example, under the conditions h of
1.34 .mu.m and materials of BaCD5 (manufactured by HOYA), it may
choose n of 1.604949 and .delta. (405 nm) of 4.0.pi. for .lamda. of
405 nm, n of 1.586051 and .delta. (660 nm) of 2.4.pi. for .lamda.
of 660 nm, and n of 1.582509 and .delta. (785 nm) of 2.0.pi. for
.lamda. of 785 nm.
[0124] Using such materials, the stair-step shaped section is
designed to correct the spherical aberration in the object lens 108
for the light beam having a wavelength of 660 nm and the spherical
aberration in the substrate of the DVD-system optical recording
medium 109b for the light beam having wavelength of 660 nm.
[0125] Therefore, when the wavefront aberration has the shape shown
in full line in FIG. 22A, because the stair-step shaped section is
designed to give a phase difference shown by dashed line in FIG.
22A, it is possible to reduce the wavefront aberration. After this
correction, the wavefront aberration is reduced as shown in FIG.
22B.
[0126] FIG. 23 shows a general configuration of an optical pickup
according to a third embodiment of the present invention. By this
optical pickup, information recording, reproduction or deletion is
performed on each of a blue-system optical recording medium, with
an operating wavelength of 405 nm, an NA of 0.85, and a
light-incident side substrate thickness of 0.1 mm; a DVD-system
optical recording medium, with an operating wavelength of 660 nm,
an NA of 0.65, and a light-incident side substrate thickness of 0.6
mm; and a CD-system optical recording medium, with an operating
wavelength of 785 nm, an NA of 0.50 , and a light-incident side
substrate thickness of 1.2 mm. The blue-system optical recording
medium is different from the first and second embodiments. It has
an operating wavelength of 405 nm, a NA of 0.85, and a
light-incident side substrate thickness of 0.1 mm. In this case, it
is possible to increase a capacity for data recording.
[0127] In the above-described optical pickup, a case where
information recording, reproduction or deletion is performed on the
blue-system optical recording medium, with the operating wavelength
405 nm, NA of 0.85, and a light-incident side substrate thickness
of 0.1 mm, will now be described. A linearly polarized beam emitted
by the semiconductor laser 101 with a wavelength of 405 nm is
transformed into an approximately parallel beam by the collimator
lens 102, and then, passes through the polarization beam splitter
103 and the trichroic prism 104. After that, the light path is
deflected 90 degrees by the polarization prism 105, and the beam
then passes through the wavelength plate 106, by which it is
transformed into a circular polarization. And after that, the beam
then passes through the wavelength selectable deflecting element
107, no effect is provided at all, and then it is incident on the
object lens 108', by which it is focused into a minute spot on the
optical recording medium 109a. Informational recording,
reproduction, or deletion is performed by this spot on the optical
recording medium.
[0128] After being reflected by the optical recording medium 109a,
the light has a circular polarization in the direction opposite to
that in the above-mentioned case of coming into the optical
recording medium. The light is transformed into an approximately
parallel beam again, transformed into a linear polarization,
perpendicular to that in the above-mentioned case of coming into
the optical recording medium, by the wavelength plate 106, and
reflected by the polarization beam splitter 103. The beam is
converged by the detection lens 110, deflected in a splitting
manner by the beam splitting device 111 into a plurality of beams,
which are then incident on the light-receiving device 112. From the
light-receiving device 112, an aberration signal, an information
signal, and a servo signal are detected.
[0129] Next, a case will now be described where information
recording, reproduction or deletion is applied to the DVD-system
optical recording medium, with an operating wavelength of 660 nm,
an NA of 0.65, and a light-incident side substrate thickness of 0.6
mm. The hologram unit 201 integrally includes a semiconductor laser
201a, a hologram 201b, and a light-receiving device 201c. The 660
nm light which comes out of the semiconductor laser 201 a passes
through the hologram 201b and thus, is transformed into an
approximately parallel beam by the collimator lens 202. Then, the
beam is transmitted through the dichroic prism 205, which transmits
light in a red wavelength zone while it reflects light in an
infrared wavelength zone, and is reflected by the trichroic prism
104, which transmits light in a blue wavelength zone while it
reflects light in a red wavelength zone, in the direction toward
the polarization prism 105. The light is reflected 90 degrees by
the polarization prism 105, and the wavelength plate 106 then
transforms the beam into a circular or elliptic polarization. The
beam is deflected for 1st order by the wavelength selectable
deflecting element 107 to make a minute spot, and the beam then is
incident on the object lens 108', by which the beam is focused into
a minute spot on the optical recording medium 109b. Informational
recording, reproduction, or deletion is performed by this spot on
the optical recording medium.
[0130] After being reflected by the optical recording medium 109b,
the beam is reflected by the polarization prism 105, reflected by
the trichroic prism 104, converged by the collimator lens 202, and
diffracted by the hologram 201b in the direction toward the
light-receiving device 201c, which is held in the same package as
the semiconductor laser 201a. From the light-receiving device 201c,
an aberration signal, an information signal, and a servo signal are
detected.
[0131] Then, a case will now be described where information
recording, reproduction, or deletion is performed on the CD-system
optical recording medium, with the operating wavelength of 785 nm,
an NA of 0.50, and a light-incident side substrate thickness of 1.2
mm. As in the above-described case for a DVD system, a pickup of CD
system also has light receiving/emitting devices all located in one
package, and, a hologram unit which separates beams using a
hologram is used generally. As such, the hologram unit 211
integrally includes a semiconductor laser 211a, a hologram 211b,
and a light-receiving device 211c, as in the hologram unit 201. A
785 nm light which comes out of the semiconductor laser 211a of
this hologram unit 211, passes through the hologram 211b, and is
made into a parallel light beam by the collimator lens 212. After
that, the light is reflected by the dichroic prism 205, which
transmits light in the red wavelength zone while it reflects light
in the blue and infrared wavelength zones, and is reflected by the
trichroic prism 104, which transmits light in the blue wavelength
zones but reflects light in the red and infrared wavelength zones,
in the direction toward the polarization prism 105. The light path
is deflected 90 degrees by the polarization prism 105. The
wavelength plate 106 transforms the light into an elliptic
polarization or a circular polarization, and the light is
controlled in its cross section into an NA of 0.50 by the
wavelength selectable deflecting element 107. The beam is deflected
for 1st order by the wavelength selectable deflecting element 107
to make a minute spot. After that, the light is incident on the
object lens 108', and thereby, it is focused into a minute spot on
the optical recording medium 109c. Informational recording,
reproduction, or deletion is performed by this spot on the optical
recording medium 109c.
[0132] After being reflected by the optical recording medium 109c,
the light is deflected by the polarization prism 105, reflected by
the trichroic prism 104, reflected by the dichroic prism 205,
converged by the collimator lens 212, and diffracted by the
hologram 211b in the direction toward the light-receiving device
211c, which is held in the same package as the semiconductor laser
211a. From the light-receiving device 211c, an aberration signal,
an information signal, and a servo signal are detected.
[0133] In the third embodiment of this invention, because the
blue-system has the NA of 0.85, the DVD-system has the NA of 0.65
and the CD-system has the NA of 0.50, it is necessary to switch
between three stages. The light beam is limited by the aperture
108c in the actuator 108b for blue-system, is limited by the
numerical aperture limiting deflecting area for CD-system the same
as in the first embodiment. The light beam is limited by a
numerical aperture limiting deflecting area for DVD-system 107f
allocated around the aberration correcting deflecting area for
DVD-system 107d.
[0134] It is preferable to use the 4 leveled stair-step shaped
section for deflecting groove the same as in the second embodiment,
for example. The numerical aperture limiting deflecting area for
DVD-system 107f transmits light in a blue wavelength zone and light
in a red wavelength zone while it deflects light in an infrared
wavelength zone. A light beam emitted from the light source and
deflected by the numerical aperture limiting deflecting area for
DVD-system 107f is scattered to avoid overlapping the focused light
spot. The light beam reflected by the optical recording medium is
deflected again by the wavelength selectable deflecting element
107. If the deflected light beam is incident on the photo detector,
it becomes noise. So it is preferable to design the pattern of the
deflecting groove to avoid overlapping with the photo detector.
[0135] FIG. 25A shows when the optical recording medium is the
blue-system one using a wavelength of 405 nm, an NA of 0.85, .PHI.
of 4.0 mm, and an infinite system incident light beam. FIG. 25B
shows when the optical recording medium is the DVD-system one using
a wavelength of 660 nm, an NA of 0.65, .PHI. of 3.2 mm, and an
infinite system incident light beam. FIG. 25C shows when the
optical recording medium is the CD-system one using a wavelength of
785 nm, an NA of 0.50, .PHI. of 2.5 mm, and an infinite system
incident light beam.
[0136] The aberration characteristic of the single object lens 108'
is optimum at the wavelength of 405 nm and the substrate thickness
of 0.1 mm, as shown in FIG. 25A. When infinite system light, with a
wavelength of 660 nm, is incident on the lens 108', and the lens
forms a beam spot on a DVD-system optical recording-medium 109b
having a substrate thickness of 0.6 mm, then the wavefront
aberration is as shown in FIG. 25B. The horizontal axis of FIG. 25B
represents the pupil radius position and the vertical axis of FIG.
25B represents wavefront aberration. FIG. 25B shows the two
dimensional cross-sectional shape of phase differential
distribution, but actually, there is a three dimensional
distribution and it has rotational symmetry around the vertical
axis.
[0137] The DVD-system light path according to a third embodiment of
the present invention has finite-system to correct the aberration.
FIG. 26A shows the relationship between the object distance and the
wavefront aberration when the light path is the DVD-system one
using an object lens. The wavefront aberration is at a minimum
around the object distance of 37 mm. FIG. 27A shows a wavefront
aberration when the light path is the DVD-system one with finite
system or infinite system using a wavelength of 660 nm, an NA of
0.64, .PHI. of 3.205 mm, and an object distance of 37.5 mm.
Although no parts are shown between the object lens and the light
source, there actually are a wavelength plate, a prism and a lens,
etc. between the object lens and the light source. In particular,
an optical pickup corresponding to 3 kinds of optical disc
(blue-system, DVD-system and CD-system) has lots of parts, so the
above described 37 mm of object distance is too short. It is a
limitation for parts alignment.
[0138] When infinite system light with a wavelength of 785 nm is
incident on the lens 108', such that a beam spot is formed on the
CD-system optical recording-medium 109c, having a substrate
thickness of 1.2 mm, then the wavefront aberration is as shown in
FIG. 25C. The horizontal axis of FIG. 25C represents a pupil radius
position and the vertical axis of FIG. 25C represents a wavefront
aberration. FIG. 26B shows the relationship between the object
distance and the wavefront aberration when the light path is the
CD-system one using an object lens which has an NA of 0.50. The
wavefront aberration becomes minimum around the object distance of
26 mm. But the object distance that minimizes the wavefront
aberration is shorter than the DVD-system one.
[0139] And above described, there is a problem from the effect
about the object lens shifts. FIGS. 28A and 28B show relationships
between the object lens shifts and the wavefront aberration. FIG.
28A shows when the light path is the DVD-system one with a finite
system. FIG. 28B shows when the light path is the CD-system one
with a finite system. It is preferable that the object lens shifts
is 0.3 mm to 0.4 mm, but especially, the deterioration in CD-system
is close to Marecial's criterion of 0.07 .lamda.rms, it is upper
limitation of wavefront aberration generally. As above described,
it is preferable to generate the incident light with an
infinite-system in a DVD-system and a CD-system.
[0140] Specification data for an object lens according to a third
embodiment of this invention is shown in the table of lens data of
FIG. 29. In FIG. 29, "OBJ" represents the object point (laser diode
used for optical source). "INFINITY" represents the curvature
radius RDY and the thickness THI means that the optical source is
located at the infinite distance. Here, all the quantities having
the dimension of length are represented by "mm."
[0141] S1 represents a surface of the wavelength selectable
deflecting element 107 at the side of the optical source, S2
represents a surface of the wavelength selectable deflecting
element 107 at the side corresponding to the optical recording
medium, S3 represents the lens surface of the object lens 108' at
the side of the optical source, S4 represents the lens surface of
the object lens 108' at the side corresponding to the optical
recording medium. S5 represents the surface of the optical
recording medium 109 irradiated with the optical beam and hence
located at the side of the optical source, S6 represents an
opposite side surface of the optical recording medium 109 and hence
located at the side of the optical source. The distance between S5
and S6 is the substrate thickness, and is 0.1 mm for the
blue-system optical recording medium, 0.6 mm for the DVD-system
optical recording medium, and 1.2 mm for the CD-system optical
recording medium. EPD represents an incident pupil diameter. WL
represents the wavelength.
[0142] The wavefront aberration in the optical system using the
above described object lens and wavelength selectable deflecting
element is 0.0072 .lamda.rms for blue-system, 0.0014 .lamda.rms for
DVD-system using 1st-order deflecting light beam, and 0.0001
.lamda.rms for CD-system using 1st-order deflecting light beam.
They are under the Marecial's criterion of 0.07 .lamda.rms. FIGS.
30A through 30C show a lens shape corresponding to the specific
data of FIG. 29. FIG. 30A is for the blue-system optical recording
medium, FIG. 30B is for the DVD-system optical recording medium,
and FIG. 30C is for the CD-system optical recording medium. In this
case, the wavefront shape for the blue-system is the same as FIG.
25A, the wavefront shape for the DVD-system is the same as FIG.
31A, and the wavefront shape for the CD-system is the same as FIG.
31B.
[0143] And as to the other example of a third embodiment, a
transmission and reflection switching means may be used instead of
the numerical aperture limiting deflecting area for DVD-system 107f
as shown in FIG. 32. Therefore, it may be used a limiting numerical
aperture coating area 107g evaporated a dichroic coating around the
aberration correcting deflecting area for DVD-system 107d to switch
the light beam diameter by transmission and reflection as shown in
FIG. 33. So, it becomes possible to transmit the light beam having
a wavelength of 405 nm and 785 nm and reflect the light beam having
a wavelength of 660 nm as shown in FIG. 32A, FIG. 32B and FIG. 32C.
The wavelength selectable deflecting element 107 is slanted so that
the reflected light beam having a wavelength of 660 nm is not
incident on a photo detector.
[0144] FIG. 34 is an internal perspective view showing a general
configuration of an optical information recording apparatus
according to the fourth embodiment of the present invention. The
optical information recording apparatus 10, according to the fourth
embodiment, also performs at least one of informational recording,
reproduction, and deletion, with an optical pickup 11, on an
optical recording medium 20. The optical recording medium 20 is
disk-like, and is contained in a cartridge 21 as a protection case.
Insertion of the optical recording medium 20 is carried out in the
direction of an arrow indicated as "disc insertion," shown in the
figure, through an insertion opening 12 in the optical information
recording apparatus 10. The disc-like optical recording medium 20
is then rotated by a spindle motor 13, and informational recording,
reproduction, or deletion is performed thereon by the optical
pickup 11. The optical recording medium 20 may be used without the
cartridge 21.
[0145] As this optical pickup 11, the optical pickup in each of the
above-mentioned first through third embodiments of the present
invention may be applied. The entire disclosure of Japanese Patent
Application No. 2004-159641, filed May 28, 2004, is incorporated
herein by reference.
* * * * *